(a) Field of the Invention
The present invention relates to a method and apparatus for estimating a channel in a mobile communication network. More particularly, the present invention relates to a method and apparatus for a channel under a channel environment where interference between neighboring base stations exists in a mobile communication network using an orthogonal frequency division multiplexing (hereinafter referred to as “OFDM”) method.
(b) Description of the Related Art
The OFDM method is a method of converting input serial symbol streams into parallel signals, modulating the parallel signals with a plurality of sub-carriers having orthogonality with respect to one another, and transmitting the modulated signals.
A partial usage sub-channel (PUSC) area transmitted from a base station of an OFDM system to a terminal is composed of a plurality of clusters. One cluster is composed of fourteen sub-carriers and two symbols.
FIG. 1 is a view illustrating the structure of one cluster according to the related art.
As shown in FIG. 1, one cluster is composed of twenty-four data sub-carriers and four pilot sub-carriers to be used to estimate a channel.
FIG. 2 is a view illustrating that channels of signals received from two base stations are estimated in the OFDM system according to the related art. In other words, FIG. 2 shows that channels are estimated using one cluster having the structure shown in FIG. 1.
As shown in FIG. 2, two pilot sub-carrier signals received from a terminal MS with respect to pilot sub-carrier signals included in PUSC clusters transmitted from a first base station BS 1 and a second base station BS 2 are expressed as in the following Equation 1.
                              y          →                =                              [                                                                                Y                    1                                                                                                                    Y                    2                                                                        ]                    =                                                    P                ·                                  h                  →                                            +                              n                →                                      =                                                            [                                                                                                              p                          11                                                                                                                      p                          12                                                                                                                                                              p                          21                                                                                                                      p                          22                                                                                                      ]                                ·                                  [                                                                                                              h                          1                                                                                                                                                              h                          2                                                                                                      ]                                            +                              [                                                                                                    n                        1                                                                                                                                                n                        2                                                                                            ]                                                                        (                  Equation          ⁢                                          ⁢          1                )            
Here, Yi represents signals received by the terminal, Pij represents the i-th pilot sub-carrier signal transmitted from the j-th base station, hi represents a wireless path gain that a signal transmitted from the i-th base station undergoes, and ni represents white noise added to the i-th received signal.
If a maximum likelihood channel estimating method that is easily implemented with respect to the received signals of Equation 1 and provides excellent performance is used, Equation 2 is given as follows.
                                                        h              ^                        →                    ML                =                                            (                                                P                  H                                ·                P                            )                                      -              1                                ·                      P            H                    ·                      y            →                                              (                  Equation          ⁢                                          ⁢          2                )            
Here, PH represents the Hermitian matrix of a matrix P, ( )−1 represents the inversion of a matrix, and (PH·P)−1 should exist for this method.
Further, a pilot sub-carrier used to estimate a channel is modulated to “1” or “−1” and transmitted. Therefore, a probability that the inversions of the matrixes of Equation 2 used to estimate channels do not exist may become very strong.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.